I come up this question due to the requirement in here .
In a short summary, I want to "display a borderless custom block on homepage only". So a custom block that is only a plain square, without anything, and I can put my html code in the cutom block. To be more specific, "borderless" means without the block title - without
 <{$block.title}>

The suggested hack is pretty good idea which could resolve my problem. However, I also read this. I think this is the best one for me, since I do not need to modify any php code, easier to maintain and upgrade.

So my solution is to make a custom block named "mainpic", and in theme.html check if block.title is "mainpic" then display the block without border:

<{if $block.title =="mainpic"}>

HTML... or an include file.
<{else}>

<{/if}>

What if I want to check:
"if (current section is homepage) and (block.title equal "mainpic")"?

Is it possible?

Thank you very much.

You can set it to be shown only on the "top page" using the block admin